Washing process using polycarboxylic acid salts

ABSTRACT

Textiles are washed with a liquid washing agent, softened water, and salts of at least one polycarboxylic acid. The polycarboxylic acids are present in part as sodium salt and in part as calcium or magnesium salt.

The invention relates to an improved washing process and new liquiddetergents.

Many processes are known for washing laundry and textiles. A detergent,as the chemical aid, and a washing machine as a mechanical aid, andwater, as the medium for taking up dirt, are usually employed (wetwashing). With the water, the so-called water hardness essentiallyformed from ions of calcium and magnesium and of sulphate, carbonate andbicarbonate, is as overall also introduced into the washing process. Thesalts interfere with the washing process, since they can form salts withwash-active surfactants and since they prevent or make difficult theremoval of stains from the goods to be washed. The water hardness isusually reduced by additives contained in the detergent, such aspolyphosphates, zeolites or laminar silicates, so-called builders. Thismeets two limits: phosphates are permitted to only a limited extentaccording to detergent legislation, and zeolites or laminar silicates,which are introduced into the wash liquor as insoluble solids, requireco-builders so that they can be rinsed out, with further water, of thegoods to be washed. However, the combination of builder/cobuilder itselfcan be rinsed out only with a minimum amount of water (50-60 l), smalleramounts of water in the main washing operation lead to deposits on thelaundry.

As an alternative to using builders, however, the water can also be atleast partly softened (for example ion exchangers, reverse osmosis,electrodialysis), which renders the use of builders superfluous.Problems occur here, however, with foaming, (cf. G. Jakobi, M. J.Schwuger in Waschmittelchemie [Detergents chemistry], Henkel & Cie GmbH(publisher) Dusseldorf 1976, p. 103) if softened water is used inparticular (and if appropriate with an overdose of the detergent), whichcan destroy the machine by an electrical short-circuit. Furthermore,softened water has to date been used for all the washing operations,that is to say also the first rinsing operation, so that since very softwater rinses the soap out of the textile less well, more water must beused for rinsing.

The invention is based on the object of providing an improved washingprocess.

The invention relates to a washing process for washing textiles withliquid detergents using softened water and salts of at least onepolycarboxylic acid, characterized in that the polycarboxylic acid ispresent to the extent of 1 to 90 mol % as the sodium salt and to theextent of 0.1 to 10 mol % as the calcium or magnesium salt.

According to the invention, it is possible to convert the polycarboxylicacid partly into the corresponding calcium salts or magnesium salts orto add calcium or magnesium salts to it, possible anions being, inparticular, sulphate, carbonate, phosphate or chloride.

In a particularly preferred embodiment, a self-metering washing machineis used. The polycarboxylic acid are the acids usually employed asbuilders, for example, polyacrylates, polymaleates and, in particular,the salts of polyaspartic acids. In a particularly preferred embodiment,salts of such a polyaspartic acid which is present to the extent of morethan 50%, in particular to the extent of more than 60%, asβ-polyaspartic acid and has a molecular weight of >500, in particular of1000 to 5000, measured by means of gel permeation chromatography inaqueous systems, are used.

The polyaspartic acid can be obtained here in the customary manner, forexample starting from aspartic acid, and in particular starting bythermal condensation on the basis of maleic anhydride and ammonia, ifappropriate via the intermediate stage of polysuccinimide, seeEP-A-256,366 (=U.S. Pat. No. 4,839,461). These polyaspartic acids areused in preference to other polycarboxylic acids, since they have goodwashing properties as builders and cobuilders, are biologicallydegradable and surprisingly form water-soluble, non-crystallizing saltswith calcium and/or magnesium ions (see above), and therefore do notprecipitate out of liquid detergents.

The detergents to be used according to the invention preferablyadditionally comprise surfactants, bleaching agents and furtherfunctional constituents, such as enzymes, optical brighteners,water-glass standardizing agents, colour transfer inhibitors, dyestuffsand perfume oils. In this context, reference is made specifically, forexample, to Hermann G. Hauthal, Chemie in unserer Ziet [Chemistry in ourtime], 1992, pp.293-303.

The following are particularly suitable for liquid metering of bleachingagents:

Hydrogen peroxide (preferred)

Sodium hypochloride

Na perborate (as a concentrated solution)

Na percarbonate (as a concentrated solution)

Na persulphate (as a concentrated solution)

Na chlorate (as a concentrated solution).

Small (≦10%) suspendable proportions of zeolite or laminar silicate canalso be added to the liquid formulation, which can be present as asolution or dispersion or emulsion, in order to introduce certain effectsuch as an activated surface and the like (soil redeposition onzeolite).

The calcium or magnesium salts to be used according to the inventionsurprisingly regulate the water hardness of the softened water via themetering in of the detergent, and thus surprisingly avoid a severe,destructive foaming.

The washing process according to the invention preferably proceeds inthe following stages:

1. Preliminary washing operation (if appropriate) to me deionized waterand an amount of detergent as predetermined (automatic metering)

2. Main washing operation with deionized water and an amount ofdetergent as measured by the development of foam in the machine(optimized amount)

3-6. Rinsing operations with water from the domestic mains

7. Last rinsing operation with deionized water.

In another preferred embodiment, steps 1, 5 and 6 are omitted.

Softened water is used only for the main washing operation and the lastrinsing operation, so that no encrustation of calcium or magnesium onthe laundry can occur during these operations. In contrast, the firstrinsing operation comprises hard water, in order to optimize rinsing andto consume little water. A special washing machine which meters in theoptimum amount of detergent in liquid form by conductivity sensors orthe like, with the aid of low foaming, is preferably employed for this.

Thus:

less detergent (surfactants, bleaching agents) is used

no or only small amounts of builders based on zeolite/laminar silicateare used

less water and therefore less (heating) energy is used.

Furthermore, the amount of sodium carbonate (builder, soluble) can alsobe reduced, and further energy can be saved by not using zeolite/laminarsilicate which are prepared from water-glass with very high expenditureof energy.

If the bleaching agent is metered in separately, it can be

less in quantity, since the (oxidizable) surfactants can be partly ormostly removed

metered in later than the remainder, and surfactants and the like canthus be saved.

We claim:
 1. A method of regulating foam in a washing process forwashing textiles with liquid detergents using softened water and saltsof at least one polycarboxylic acid, wherein the polycarboxylic acid ispresent to the extent of 1 to 90 mol % as the sodium salt and to theextent of about 10 mol % as the calcium or magnesium salt and furtherwherein the salts of the polycarboxylic acid reduce the amount of foamthat is generated during the washing process.
 2. A method of regulatingthe foam in a washing process according to claim 1, characterized inthat the polycarboxylic acid is a polyacrylic acid, polyacrylomaleicacid or polyaspartic acid.
 3. A method of regulating the foam in awashing process according to claim 1, characterized in that thepolycarboxylic acid is a polyaspartic acid, the proportion of β-linkagesof which is >50% and which has a molecular weight of 500 to
 5000. 4. Amethod of regulating the foam in a washing process according to claim 3,characterized in that the polyaspartic acid has been obtained by thermalpolycondensation of maleic anhydride or maleic acid and ammonia.